1. Field of the Invention
The present invention relates to a hydraulic pressure intensifier with a supply connection, a return connection, a high-pressure connection, an intensifier piston assembly including a high-pressure cylinder with a high-pressure piston displaceable therein and a low-pressure cylinder having a greater cross-section than the high-pressure cylinder, with a low-pressure piston which is displaceable in the low-pressure cylinder and is connected to the high-pressure piston and divides the low-pressure cylinder into a first low-pressure chamber on the side of the high-pressure piston and a second low-pressure chamber, and with a switching valve which either acts on the second low-pressure chamber with pressure from a pressure source or relieves it of pressure, wherein the switching valve includes a valve element which in one direction of movement is subjected to a pressure in a first control pressure chamber with a smaller pressure application area and in the opposite direction of movement is subjected to a pressure in a second control pressure chamber with a larger pressure application area.
2. Description of the Related Art
A hydraulic pressure intensifier of this kind is known from DE 196 33 258 C1.
The high-pressure cylinder is supplied with fluid from the supply connection via a first non-return valve when the high-pressure piston moves in a direction which increases the volume of the high-pressure cylinder. Upon a decrease in volume of the high-pressure cylinder, this fluid is then discharged via a second non-return valve to the high-pressure connection. The movement of the high-pressure piston is controlled by the movement of the low-pressure piston. The low-pressure piston is subjected to pressure from the supply connection on its side facing away from the high-pressure piston when the volume of the high-pressure cylinder is to decrease. When the volume of the high-pressure cylinder is to increase, this takes place under the pressure of the fluid flowing into the high-pressure cylinder. In the process, the fluid located in the second low-pressure chamber of the low-pressure cylinder is displaced partly to the return connection and partly into the first low-pressure chamber. For this purpose, the second low-pressure chamber is rendered pressureless. Switching of pressurization of the two low-pressure chambers of the low-pressure cylinder is effected via a switching valve with a valve element which is constructed as a valve slide. One end face of the valve element is subjected to the pressure in a control pressure chamber, wherein this pressure corresponds to the pressure at the supply connection. This first control pressure chamber acts with a smaller pressure application area on the valve element than the pressure in a second control pressure chamber on the opposite side of the valve element. This pressure changes. In the known case it is controlled by the movement of the high-pressure cylinder. As the pressure in the second control pressure chamber acts via a larger pressure application area on the valve element, the valve element is subjected to the changing pressures in the second control pressure chamber in such a way that it can be moved to and fro in the correct position.
This design functions to a large extent satisfactorily. However, it presupposes that the fluid which is to be raised to a higher pressure is identical with the fluid which is used for xe2x80x9cdrivingxe2x80x9d. Separation of the two fluids is not possible.
It is the primary object of the present invention to provide a pressure intensifier in which the driving fluid can be different from the pumped fluid.
In accordance with the present invention, this object is met in a hydraulic pressure intensifier of the kind described above by the fact that the pressure in the second control pressure chamber is controlled by the low-pressure piston.
Thus, the high-pressure piston is used as a xe2x80x9csealing zonexe2x80x9d between two fluid zones which accordingly can admit different fluids. Naturally, it is also possible to drive the pressure intensifier with the same fluid which is also to be pumped. The possible applications have however been extended appreciably when pressure in the second control pressure chamber is controlled by the low-pressure piston. The characteristic of the control pressure chambers being arranged on opposite sides of the valve element in the direction of movement is to be understood functionally here. The valve element is controlled or moved by the pressure in one control pressure chamber into one switching position and by the pressure in the other control pressure chamber into another switching position. How this is effected in detail depends on the design of the valve element, e.g. whether it is constructed in one or more parts.
Preferably, the second control pressure chamber is connected to a pilot line comprising two branches which at two positions axially remote from each other open out into the circumferential wall of the low-pressure cylinder. Of the two branches, one ensures that the second control pressure chamber is subjected to an elevated pressure, for example, the pressure at the supply connection, while the other branch is used to relieve the second control pressure chamber of pressure. Control is here effected exclusively by the low-pressure piston which, depending on the position, alternately either closes or clears the openings of the two branches.
Preferably, the low-pressure piston includes an auxiliary channel which in one position of the low-pressure piston comes into alignment with the opening of one branch and in another position of the low-pressure piston comes into alignment with the opening of the other branch. Preferably, the two positions are the end positions of the low-pressure piston, i.e. the positions in which the high-pressure cylinder has its greatest or its smallest volume. Due to the fact that it is not the end edge of the low-pressure piston, but an auxiliary channel located in or on the low-pressure piston that is used for pressure control, it is no longer required to use the pressures in the first or second low-pressure chamber to switch the valve element of the switching valve assembly. This facilitates control of the switching valve very considerably.
Preferably, the auxiliary channel is formed by a circumferential groove on the low-pressure piston. The circumferential groove can be made easily. It does not lead to significant weakening of the low-pressure piston. Above all, it is favorable that angular adjustment of the low-pressure piston is no longer required. The low-pressure piston in practically any rotational position is capable of making a connection between the openings of the two branches and the auxiliary channel.
Preferably, a supply channel connected to the supply connection opens out at the same axial position as the opening of the first branch, and a return channel connected to the return connection opens out at the same axial position as the opening of the second branch. Through the auxiliary channel, therefore, the connections between the second control pressure chamber and the supply connection, on the one hand, and the return connection, on the other hand, can then be made in a relatively simple manner. Pressurization of the second control pressure chamber is then effected only for a short time, i.e. as long as the auxiliary channel, the two branches and the supply channel or return channel come into alignment with each other; but this short time is sufficient to cause the valve element of the switching valve assembly to switch. Thereafter the pressure in the second control pressure chamber is essentially trapped, so that pressure variations in the supply connection or in the return connection can no longer have an effect on the position of the valve element.
Preferably, a stop plug is arranged between the second control pressure chamber and the supply connection. This stop plug or throttle ensures that the pressure in the second control pressure chamber can remain at the pressure of the supply connection even if leaks occur. These leaks, if any, are as a rule so small that the fluid continuing to flow through a stop plug is sufficient for equalization. If, on the other hand, the pressure in the second control pressure chamber has been relieved to be equal to the pressure at the return connection, then the fluid continuing to flow through the stop plug does not lead to a pressure increase in the second control pressure chamber fast enough to be able to displace the valve element.
It is particularly preferred that the stop plug is arranged in a line which can be shut off. The delivery of fluid under pressure into the second control pressure chamber can therefore be prevented if this is not wanted. Conversely, it can be ensured that leaks are equalized if the higher pressure prevails in the control pressure chamber, so that the valve element is reliably held fast in both its positions. Hence the pressures defined by the low-pressure piston in the second control pressure chamber for the respective positions of the valve element are trapped.
Preferably, the line which can be shut off is controlled by the valve element. Thus, external measures are not required and the correct switching state can always be produced automatically when the valve element changes its position. In the position in which the second control pressure chamber has been placed under pressure, a connection of the supply connection to the second control pressure chamber is then made automatically via the stop plug. Conversely, this connection is interrupted when the second control pressure chamber has been rendered pressureless.
It is particularly preferred that the stop plug is arranged in the valve element. This is a relatively simple option for clearing or shutting off the line in which the stop plug is arranged, depending on the position.
Preferably, the stop plug branches off from a channel which, in a position of the valve element caused by the pressure in the second control pressure chamber, connects the supply connection to the second low-pressure chamber. This is a relatively simple embodiment. Alterations to the housing of the switching valve assembly are not necessary. Basically, an additional bore in the valve element is sufficient.
Preferably, the high-pressure connection is connected via a pilot-controlled non-return valve to the return connection. This embodiment is advantageous if the driving fluid is the same as the one which is also to be raised to a higher pressure. One is then able to relieve the high-pressure side of pressure relatively rapidly.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.